The match in Benguela is followed by the last of the quarter-final clashes between Nigeria and Zambia in Lubango.
Both Egypt, who also defend a record-breaking 16-match unbeaten run at the Nations Cup finals stretching back six years, and Cameroon were sweating on the fitness of key players before the match at the Ombaka Stadium.
Egypt captain Ahmed Hassan has not trained for the last three days as he nurses a calf strain. He could make an African record 170th international appearance on Monday.
Cameroon's captain Samuel Eto'o practised only briefly with his team on Sunday as he was suffering from a sore toe, officials said.
The match winners will stay in Benguela and play against Algeria in the semi-finals on Thursday.
Nigeria start as favourites in Lubango against the Zambians, who surprised many by topping Group D in the first round.
Nigeria play without injured captain Joseph Yobo but are in much better mood after recovering from losing their opening game against Egypt.
Zambia's only win at the tournament came in their last Group D game on Thursday when they edged Gabon 2-1, a result that proved enough to elevate them to the top in their standings.
The winners of the Lubango encounter go to Luanda to meet Ghana, who knocked out hosts Angola in the quarter-finals, for a place in the final.
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